1. Field of the Invention
The present invention relates to pump rotors including walls of relatively small thickness and made of injected thermoplastic material for the displacement of different fluids (oils, greases, hydrocarbons, air, and the like). The present invention also relates to a process of manufacturing the pump rotors described above.
2. Description of the Prior Art
Pump rotors made of metal walls of small thickness, for instance, by assembling parts cut from a metal sheet or produced by precision pressure casting, are well known. It is tempting for the person skilled in the art to replace the metal in these products by plastic, a material which is more inert chemically and less dense. Thus, forming the rotor of plastic makes it possible to reduce the mass of the moving parts of the rotor and less expensive to manufacture, thereby making it possible to reduce the total cost. However, parts made of plastic have less mechanical strength than metal parts, thereby creating a need for walls of increased thickness when forming the walls of plastic. In addition, parts made of plastic are not as dimensionally precise as parts made of thin metal. Plastic parts also have poorer thermal stability and durability than metal parts.
It is also difficult to obtain an assembled unit which is satisfactorily and permanently balanced whether one uses metal parts or molded parts. It is usually necessary to individually balance each of the rotor parts after assembly.
The technique of monobloc injection of plastic materials with fusible cores would make it possible to obtain suitable shapes of blades for this type of rotor (hollow shapes, warp shapes and undercut shapes). However, such a technique would not be precise enough to assure relatively constant, small wall thicknesses. Here again, the problem of balancing would arise in the case of rotors rotating at high speed (more than 1000 rpm, for instance). French 2 604 116, which relates to a process for manufacturing an impeller wheel for a coolant pump of an automotive vehicle is one example of this technology.